Listed here are some ideas for development projects. You might have some additional ideas and that's wonderful but if you are stuck for a basis for a new project, start here. There is a need in some way or other regarding these suggestion and the basis is described in each.
1. Microcomputer development bed
When designing a project, it is often handy to have a univsersal (or nearly so) development environment. A software IDE (Integraded Development Environment) normally handles the software but the hardware is often just too complex for you to rework it each time you have a software change. Thus, a universal development environment is a dream for most designers. A microcontroller with 24 or more input/output pins which can be used as either means that decoders and encoders should be present in abundance and selectable by the designer. That's a pretty tall order and it makes your design complex. It can be very worthwhile when complete though. Personally, I struggle with this all the time because I never feel as if I am finished.
2. Radio Control Equipment
Most off the shelf control systems for cars, boats and planes are adequate to their tasking for most hobbyists. I like the idea of full telemetry between the devices O control and my equipment. A universal dashboard with reassignable displays would be ideal as well as lightweight sensor and transceivers in the remote equipment. Being able to know the engine RPM, on board fuel quantity and speed would be a great start. In a rocket, full telemetry would be so like NASA as to frighten most hobbyists. But it is a goal that is attainable.
3. Model Railroading
Since most model railroads are electrically operated it only follows that a control system would be electrical or wireless. For the remaining live steam, gasoline or diesel trains, a wireless control system would be ideal. In addition to starting/stopping and speed control, we should consider remote switching, signal systems, building control and load handling. For the indoor electrical systems, DCC (Digital Command Control) systems are becoming popular but the high price ($500 and upward) of these basic systems is making it a very elite branch of the hobby. The goal in DCC would not be to create a better system but to focus on making it less expensive and thereby more affordable.